Differential Capacity Voltage Relaxation Analysis for Detecting Low Temperature Plating
Differential capacity voltage relaxation analysis detects sub-zero lithium plating by identifying chemical re-intercalation peaks during post-charge rest.
Low Temperature Fast Charge Qualification
Meaning
Electrothermal validation programs for lithium-ion cells determine the safe charging limits of battery chemistries under freezing conditions. Performing a low temperature fast charge qualification establishes the specific current and temperature thresholds where charging can occur without causing cell damage. This evaluation is necessary to develop the safe operating limits for electric vehicle battery packs.
Test Procedure
Testing involves cycling the cells in environmental chambers kept at temperatures below zero degrees Celsius using high charging currents. Engineers measure the capacity retention and internal resistance after a series of these fast charge cycles. The cells are then disassembled and analyzed to check for lithium plating on the graphite anode.
This physical inspection is the most reliable way to confirm that the charging protocol has not caused internal degradation.
Electrochemical Risk
Diffusion of lithium ions into the anode graphite slows down as temperature drops, creating a bottleneck during fast charging. When the charge rate exceeds the diffusion speed, lithium ions accumulate on the anode surface and form metallic lithium. This metallic plating can grow into dendrites that penetrate the separator and cause internal short circuits.
In addition to creating safety risks, this plating rapidly reduces the available capacity of the cell.
Commercial Decision
Automotive manufacturers use the results of low temperature fast charge qualification to select the right cells for vehicles sold in cold climates. Sourcing teams compare the performance data of different cell suppliers to choose the chemistry that offers the best charging speeds without compromising long-term reliability. Contracts are awarded to suppliers whose cells can withstand these stressful charging conditions with minimal degradation.
This qualification protects the car maker from high warranty costs caused by battery degradation in winter. It also provides the necessary programming parameters for the battery management system to adjust charging rates based on real-time temperature readings.